Silver halide emulsion materials with all their enormous advantages in sensitivity, spectral sensitization and capability of producing black-and-white and color images with strong optical density and high resolving power have the drawback of requiring in conventional processing several processing liquids and a time consuming drying for the final image. Particularly the fixing and rinsing steps are of relatively long duration when archival image quality is desired. Moreover, exhausted fixing liquids and even wash liquids containing dissolved silver pose an ecological problem because draining of silver ions into the sewer is permitted only in a very limited quantity. Further, silver recovery from fixing liquids in large scale processing is nowadays a must for its economic importance and proceeds by the deposition of dissolved silver as metal or silver precipitate from the fixing liquid bulk.
Under the impulse of these specific drawbacks and requirements associated with the conventional processing of photographic silver halide emulsion materials there has been a constant search for a rapid ecologically clean processing which is as dry as possible and offers archival high quality images.
In a successful rapid access processing known as diffusion transfer reversal (DTR-) processing [ref. Photography--Its Materials and Processes--by C. B. Neblette--6th ed. D. Van Nostrand Company--New York (1962), p. 3721] an exposed silver halide emulsion material is developed in the presence of a silver halide solvent. Hereby the non-developed silver halide is complexed and transferred by diffusion into an image-receiving material to form therein a silver image by reduction with the aid of a developing agent in the presence of minute amounts of so-called development nuclei, e.g. colloidal silver or heavy metal sulphides.
Many efforts and much research were devoted to obtain diffusion transfer images of high quality in the image receiving material with reduced amount of silver halide in the light-sensitive material as compared with the conventional processing. These efforts and research directed to a large choice of development nuclei, black-toning agents, binding agents, etc. . . . , led for many purposes to satisfactory image quality in the image receiving material. However, in some fields of photography, e.g. the graphic arts and micrography, where in some applications particular sharpness, high resolving power or other extreme sensitometric qualities are required the formation of the final image in the photosensitive material by conventional processing, i.e. image formation not based on diffusion transfer of image forming substances. is still preferred.
In U.S. Pat. No. 3,179,517 and published European Patent Application 0 221 599 processes for developing and fix1ng a photographic silver halide emulsion material with a minimum of processing liquid in combination with a processing or receptor web comprising a silver complexing agent and silver ion precipitating agent, e.g. zinc sulphide for use in a conversion reaction forming a silver sulphide precipitate, are described.
The above described processes operating with fairly small amounts of liquids and a processing element containing the necessary chemicals for fixing an image-wise exposed silver halide emulsion material have the advantage to make a washing or rinsing step not absolutely necessary.
However, if a washing or rinsing step is omitted under conditions of fairly high relative humidity, e.g. 80 % relative humidity, and elevated temperature, e.g. 35 .degree. C., silver images obtained from a developed silver halide emulsion, particularly those silver halide emulsions containing some silver bromide, undergo a degradation in that viewed under diffuse light conditions light straying spots appear as black spots in the silver image parts having a relatively low optical density (i.e. in the silver image parts having an optical density in the range of 0.05 to 0.5). Said light straying spots are particularly disturbing in micrograph enlargement by severely degrading the image quality of the obtained enlarged images. It has been experimentally established by us that the light straying spots correspond with rather coarse silver halide crystal grains formed by re-halogenation, in particular re-bromination, of silver metal particles obtained in the development.